WSP06806

• File Number: 8276.450
• Description: McElmo Creek Unit - Colorado River Salinity Control Program
• State: CO
• Basin: Colorado Mainstem
• Water Division: 7
• Date: 5/1/1982
• Title: Possible Improvements for Onfarm Irrigation Systems to Reduce Salinity
• Water Supply Pro - Doc Type: Report/Study

MAY JOR~

Coordination of study activities leading to analysis of the salt

loading problem in the McElmo Creek Unit was accomplished through a

Multi-Objective Planning Team under leadership of the Bureau of Reclamation.

Participants in this team effort included personnel from the Bureau of

Reclamation, Soil Conservation Service, U.S. Fish and Wildlife Service, U.S.

Geological Survey, Colorado Division of Wildlife, Colorado Water

Conservation Board, Colorado Department of Health and the Dolores Soil

Conservation District.

Mancos shale, a marine formation with high salt content, underlies much

of the valley (See Figure 111-2) and is the principal source of salt in the

McElmo Creek Unit. Lenses of crystalline salt often are exposed during

excavation into shale. Because of the arid climate salts have not been

leached naturally and applying irrigation water to the soil greatly

accelerates the leaching process.

The McElmo Creek contributes about 115,000 tons of salt annually to the

Colorado River. About 54,000 tons are attributed to the onfarm portion of

current irrigated agriculture which was first introduced into the valley

about 70 years ago. Most of the salt is leached from the soil and

underlying Mancos shale and carried to the river by deep percolation from

irrigation and by seepage from earthen ditches.

Improved management of irrigation water including devices for measuring

water onto the fields and lining onfarm and off-farm ditches has the

potential for reducing the river's salt load by as much as 32,000 tons,

reducing salinity concentration of the Colorado River at Imperial Dam by 3.6

milligrams per liter. These impacts are based on the assumption that

improvements will be made on about 70 percent of the irrigated area. The

remaining irrigated land may not be improved under voluntary participation

in the salinity control program because of land use changes or 06~\8'1'9ns

of the individual land owners.

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